1. Field of the Invention
The present invention relates to the recognition of a fingerprint image.
2. Description of the Related Art
Conventionally, in a fingerprint matching, as a fingerprint matching apparatus noted in Japanese Laid Open Patent Application (JP-A-Showa, 59-778) or in its U.S. Pat. No. 4,646,352, a minutia matching has been widely used by using the end point and bifurcation of a fingerprint ridge (either of them is referred to as a common word “minutia”).
In the conventional technique, it is difficult to accurately distinguish minutiae from incipient ridge lines and sweat pores. The “incipient ridge line” means the growing line that does not become the ridge perfectly.
As one of the conventional techniques for processing a low quality fingerprint image containing a noise, Japanese Laid Open Patent Application (JP-A-Heisei, 8-287255) or its U.S. Pat. No. 6,018,586 discloses an apparatus and an image processor for extracting image features of a skin pattern.
The apparatus of this conventional technique includes an image feature extracting apparatus of a skin pattern image for extracting an image feature in a plurality of local regions set on an image in advance. The image feature extracting apparatus has an image memory, a group of filters memory, an image magnitude calculator and a feature calculator.
The image memory stores a skin pattern image. The group of filters memory stores a plurality of filters composed of a two-dimensional array of weighting factors to extract the image features in the local regions. The filtering means filters the skin pattern images stored in the image memory by using the plurality of filters stored in the group of filters memory, respectively. The image magnitude calculator calculates the image magnitudes in the plurality of local regions set on the images in advance, for the respective images obtained by the filtering device. The feature calculator uses the information of the image magnitudes of the local regions which are obtained by the image magnitude calculator and then calculates the image features in the respective local regions.
According to the method proposed in the Japanese Laid Open Patent Application (JP-A-Heisei, 8-287255) or in its U.S. Pat. No. 6,018,586, the plurality of two-dimensional filters having the weighting factors, which correspond to the image features of ridge directions and ridge pitches are prepared in advance, and the filters are used to carry out a filter enhancement. Then, the result of the filtering process having the maximum image magnitude is selected, thereby executing the effective image enhancement and also extracting the ridge direction and ridge pitch, which correspond to the selected filter, as the image feature. Consequently, the noise is removed.
Also, although the conventional techniques for removing the sweat pores from the fingerprint image have been variously proposed, most of them use the supposition that the sweat pore is surrounded with ridge pixels. For example, Japanese Laid Open Patent Application (JP-A-Heisei, 5-205035) discloses a fingerprint matching apparatus.
This fingerprint matching apparatus is provided with a fingerprint sensor, a fingerprint image memory, a gray-scale image corrector and a main body device.
The fingerprint sensor scans a fingerprint image. The fingerprint image memory temporally stores a fingerprint image data read by the fingerprint sensor. The gray-scale image corrector calculates a contour line of the gray-scale image of the fingerprint from the fingerprint image stored in the fingerprint image memory. Then, false minutiae, such as an island, a bridge, a sweat pore or the like are extracted from the image constituted by the contour lines, and if the minutia is the island or bridge, the density of the portion corresponding to a closed curve surrounded with those contour lines is decreased. On the other hand, if those minutiae are the sweat pores, the density of the portion corresponding to the closed curve surrounded with those contour lines is increased and the false minutiae are removed from the gray-scale image.
As another conventional technique, Japanese Laid Open Patent Application (JP-P2001-14464A) discloses an apparatus for fingerprint image processing and the method for the same. This technique has a filtering means for eliminating sweat pores from a fingerprint image.
As still another conventional technique, Laid Open Patent Application (JP-P2001-243467A) discloses a sweat pore portion judging apparatus. This technique has an algorism for distinguishing sweat pores from islands by using the direction of ridge line.
As yet still another conventional technique, Japanese Laid Open Patent Application (JP-A-Heisei, 1-213757) discloses a sweat pore eliminating processing apparatus.